Obsessing over VD

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Cletis

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OH
Ive been a little over the top lately
Trying to make all my circuits are 4% or less (pref 3% but thats tough). Been oversizing conductors based on loads and splicing every device with linesman with only single pigtail to devices. Anyhow, ive lately been running 10/2 on long runs to a j-box then branch out some 12-2 to appliances for example. I usually just land the 10 on the
20 amp ocpd and never been turned down. I cant recall if i am supposed to downsplice 10-12 then in breaker by code or not. It makes no sense since it would be adding more resistance anyhow but any code article on this??


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Wiring to account for voltage drop is only a suggestion, a fine print note. The only hard and fast code rule is you must supply voltage to equipment within the manufacturers tolerances. I'm sure someone will correct me if I'm wrong.;)
 
Cletis said:
Ive been a little over the top lately
Trying to make all my circuits are 4% or less (pref 3% but thats tough). Been oversizing conductors based on loads and splicing every device with linesman with only single pigtail to devices. Anyhow, ive lately been running 10/2 on long runs to a j-box then branch out some 12-2 to appliances for example. I usually just land the 10 on the
20 amp ocpd and never been turned down. I cant recall if i am supposed to downsplice 10-12 then in breaker by code or not. It makes no sense since it would be adding more resistance anyhow but any code article on this??
Click to expand...

In general there is no reason you cannot downsize when you have upsized for voltage drop. As long as the overcurrent protective device is rated the same or lower then the lowest conductor ampacity.

For further help, check out this site. Voltage drop and the NEC
 
Cow said:
Wiring to account for voltage drop is only a suggestion, a fine print note. The only hard and fast code rule is you must supply voltage to equipment within the manufacturers tolerances. I'm sure someone will correct me if I'm wrong.;)
Click to expand...

Let me just add a small note to your post:

Barring fire pumps (695) and sensitive electronic equipment (647), "Wiring to account for voltage drop is only a suggestion, a fine print note."
 
Cletis, you ever wonder why most manufacturers 20 amp breakers will accept conductors up to #10 and even larger if there was a code against doing so? For example

Roger
 
I install submersible pumps. Because of the distances between the submersible motor and the service, voltage drop becomes very important. Most sub motor manufacturers publish wire size charts to determine wire sizing to keep voltage drop below 5%.

As as I recall, without looking it up, the recommended maximum voltage drop is 3% for either feeders or branch circuits, and 5% combined feeder & branch circuit.

I've made myself an excel spreadsheet to calculate minimum wire sizing based on voltage drop. I insert input amperage, voltage, length in feet and al or cu, it calculates the Minimum Circular mills required. I then have NEC table 310.15(B)(16) there and I can pick the wire size needed based on the largest required for either amperage or circular mills. It also calculates my 125% for input wiring size for a vfd, and my 115% for minimum breaker size. Then it also has NEC table 250.122 to show me to show me my grounding conductor size. Print it off, and I've got a record of the calculations.
 
Two or more different cable sizes can be used.

Franklin Electric's AIM manual gives instructions on calculating allowable voltage drop using 2 or more wire sizes.

For example, last month I installed a 10 hp 460v 3ph pump 500 ft deep in a well for a 7,500 head dairy. NEC table 439.250 says a 10 hp 460v motor has 14.0 FLA. Then table 310.15(B)(16) says I'm ok with #14. But I haven't taken into account voltage drop. And I've got the 500 ft length the motor is in the well, PLUS the 250 ft from the well to the pump house and service entrance. Here is where I go to the Franklin Electric AIM manual table 17. It says yes I can use #14 wire, but only for a maximum length of 310 ft, service entrance to motor. If I use #10 wire, my maximum allowable length is now 790 ft, just barely long enough. So what did I use? I ran 500 ft of #10 double jacketed submersible wire in the well. Then I ran the 250 ft from the well to the pumphouse with #8 in 1" PVC conduit. The pump is controlled by a Yaskawa IQ1000 VFD in PID mode. There is a TCI V1K DV/DT output filter on after the drive because of the distance from the vfd to the motor. This is one of three wells being controls from this pumphouse. A 60 hp, a 40 hp, and the 10 hp I installed.
 
Cletis said:
I usually just land the 10 on the
20 amp ocpd and never been turned down. I cant recall if i am supposed to downsplice 10-12 then in breaker by code or not. makes not sense, since it would be adding more resistance anyhow but any code article on this??
Click to expand...

roger said:
Cletis, you ever wonder why most manufacturers 20 amp breakers will accept conductors up to #10 and even larger if there was a code against doing so? For example

Roger
Click to expand...

Don't give the CMP any ideas. It's long been believed that if you mention the devil that he will appear.
 
Also need to pick where limiting VD makes sense. A piece of equipment that has it's performance deteriorated by excessive VD has a greater need for limiting VD.

VD does raise energy efficiency concerns, but at same time a load that runs 24/7 could have more associated waste more energy then a load that only sees a few hours of operation a month.
 
Cletis said:
Ive been a little over the top lately
Trying to make all my circuits are 4% or less (pref 3% but thats tough). Been oversizing conductors based on loads and splicing every device with linesman with only single pigtail to devices. Anyhow, ive lately been running 10/2 on long runs to a j-box then branch out some 12-2 to appliances for example. I usually just land the 10 on the
20 amp ocpd and never been turned down. I cant recall if i am supposed to downsplice 10-12 then in breaker by code or not. It makes no sense since it would be adding more resistance anyhow but any code article on this??


Sent from my iPhone using Tapatalk
Click to expand...


If you're asking if you have to splice a #12 pigtail onto a #10 homerun in the panel to stick in the 20A breaker, the answer is no. The only time you'd have to splice to a smaller wire there is if the breaker wont accept the larger wire, say re-purposing a 50A 240V range circuit with #6 into a 15A 120V receptacle for a gas stove.
 
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